My ‘17 Sierra 8-Speed experience

99Mastercraft · September 29, 2018

Good evening guys,

I read a lot on the forums and I just wanted to come and share my experience that i have had with GM. (Long time Chevy owner)

I purchased a 2017 GMC Sierra All terrain edition with 48k miles when I purchased. (5.3L, 8 Speed trans)

When i first bought the truck I had no knowledge about the 8 speed issues, nor did the truck have issues OR I wouldn’t have spent well over 30k on the truck.

It began with random clunking and rough shifting from 1-2 and random clunks. I took it to the dealer and they stated the shift points were off and updated the TCM and did a fast adapt relearn (I think that’s what you call it) Service manager said my VIN didn’t apply for the flush..

52,000 miles... the issue is still present, the truck lunges hard when being placed in reverse and still clunks and now I hear clunking when slowing down and downshifting..

I know that my warranty is close to expiring due to miles, so I called GMC Customer Care and started a ticket. The dealership reached out to me and the service manager called me and said to bring the truck in...

Received a phone call stating that the shop foreman duplicated the issues and believe something is wrong or broken internally in the transmission and they are pulling the transmission.

I don’t have any clue as to what they will find, but I am glad they found something. Now I hope it is covered under power train. I also hope they get my truck put back together the right way...

I found it ironic that they put me in a 2019 with 4K miles (6 speed trans) and I hear similar clunks in the drivetrain in this truck.

I didnt create the thread to bash GM, I really do hope they take care of the issue... but just as a friendly reminder to get your trucks in the shop before it’s too late. Lord knows what kind of situation I would be in at 60,001 miles

I will post updates as I hear from the shop

seamus2154 · September 30, 2018

I had a 14, and 15 both 6 speeds...both clunked and didn't ever know what gear to be in. Then I bought a 15 6.2- 8 speed. Shudder, delayed engagement clunking, feeling like being rear ended. Needed a stator shaft, and torque converter and 3 reprograms! Still wasn't right. Then a '17 6.2 8 speed. The 17 has been great now at 16K. Better than all the others but......lately I have been getting some clunking and banging. I believe GM has some of the worst trans programming. Driving habits can really add to the clunking. At 16K my feeling of having a good one is fading......

Supposedly starting in '17 most was worked out with programming, new fluid, and new torque converters??? Most big issues were the 15 and 16.

Nasty · September 30, 2018

5.3 8spd is the worst. See if you can have the trans tuned

NWI Denali · September 30, 2018

All manufacturers have areas where they clearly lead and areas where they lag behind. So pick your poison. GM just doesnt seem to do transmissions well. As others have already stated, even the 6L80 is clunky and herky jerky. And that trans has been around since what, 2009?

Nasty · September 30, 2018

18 minutes ago, NWI Denali said:

All manufacturers have areas where they clearly lead and areas where they lag behind. So pick your poison. GM just doesnt seem to do transmissions well. As others have already stated, even the 6L80 is clunky and herky jerky. And that trans has been around since what, 2009?

6l80 has been flawless for me with a 5.3. Our 8l90e is garbage

Gagliano7 · October 2, 2018

My 2018 8 speed 6.2 gmc is fine no problems.I have had the range to turn off afm since day 3 not sure if that made a difference. Trans has been great so far.

ram1067 · October 3, 2018

must be only the 5.3......cuz mine is always searches for a gear at low speeds.

sigmonster · October 3, 2018

I have 2017 Sierra 6.2/8 speed NHT that developed "the shudders" at 25,000 miles. They changed the transmission fuid but no change. Torque converter was changed 2 weeks ago. Now it is incredibly smooth. There still occasional light clunks between 1-2 gear in parking lots, but I think most 8 speeds do that.

I read somewhere that when making the torque converter, the manufacturer was damaging an internal seal and fluid was not flowing properly and that the new torque converters have a different part #. I'm not sure if all of that is true, but I would hate to have to replace torque converters every 25-50,000.

Grumpy Bear · October 3, 2018

On ‎9‎/‎30‎/‎2018 at 1:21 PM, NWI Denali said:

All manufacturers have areas where they clearly lead and areas where they lag behind. So pick your poison. GM just doesnt seem to do transmissions well. As others have already stated, even the 6L80 is clunky and herky jerky. And that trans has been around since what, 2009?

80,000 on my 6L80E without issues. My old TH-700R was a stinker. Eventually that was cured. Some were, some weren't. It will always be like that as long a imperfect humans are building imperfect machines.

71_340 · October 3, 2018

I must be one of the lucky ones, the 8-speed transmission in my 2017 Denali 6.2L shifts smooth. I bought the CPO with a little under 16K miles so if something should happen I have plenty of warranty.

99Mastercraft · October 4, 2018

Update:

Dealership called me 10/2/18 and said they were putting a transmission in the truck. Received another call today and said the transmission was on back order and they should have it next week...

I can not wait to hear what is wrong with the transmission. I feel a little sense of relief, but I hope the torque converter is alright?

Geez this has been stressful

71_340 · October 4, 2018

As unfortunately and inconvenient as that might be for you, at least your dealer and GM is taking care of it without giving you the runaround. Heh, in the end these things are put together by humans so mistakes can happen.

pd59 · October 4, 2018

My 2018 Chevy 4x4 has a 6 speed in it, and a few weeks ago my transmission gave out on me. I went to leave a parking space and the truck lurched and started making terrible grinding and whining sounds. Took it to the dealer, and they ended up replacing several internal components of the transmission. They told me that 4-6 gear planetary gears came apart, and the resulting metal shavings took out a bunch of things, such as the TC, some clutches, fluid pump, the list goes on. Truck had a little over 27k miles on it at the time. Warranty covered all of the work.

Anyway, the point of all that is once I got the truck back, the transmission has been acting similar to how you describe in your post. Shifts feel a bit wonky, sometimes it feels like it downshifts prematurely, hard up and downshifts, etc. I recall the dealer told me they adjusted the shift points. After a few days I called them and they said to give it 5k miles or so, that it needed to re learn and adjust to my driving habits, and it should clear up. Well, I'm at 31k, still acts up. I'm a little annoyed.

DanY · October 4, 2018

I just had my 15 High Country 6.2L 8-speed to the dealer yesterday for the torque convertor shutter. It just started at a bit under 13K mile. They did the flush procedure and that seems to have fixed it for now.

I was really confused what the fluid flush accomplished but I read in another topic that the initial wear of the transmission clutch packs is sending clutch material into the torque convertor and gumming it up. They stated that it looks like fine black sludge if you tear apart the transmission. This makes sense why to do the flush. The TSB states to flush the cooler lines and then drop the pan and drain the fluid. This will get most of the fluid out except for the torque convertor. As far as I know there is no way to flush a torque convertor. That is why they do multiple fill, run, and drains in the TSB. This is the only thing to me that makes sense.

If the flush doesn't fix the problem, then they replace the torque convertor.

Edited October 4, 2018 by DanY